The present invention relates to a method and apparatus for extending heater life, and specifically to a method and apparatus for extending the life of a brittle heater within a non-vacuum semiconductor processing chamber.
Many common semiconductor devices require vertical surface features (i.e., vias, trenches, holes or other similar topographical features) in order to connect distinct planes of material (e.g., for device electrical connections) or to increase device surface area (e.g., for capacitors). With shrinking lateral device dimensions, vertical surface features have become increasingly important for maintaining adequate device surface area by replacing horizontal (e.g., planar) surface area with vertical (e.g., three dimensional) surface area.
During the formation of vertical surface features, deposited material can cling to the side walls of these features, blocking deposited material from reaching the lower surfaces of the features and causing formation of hollow areas (voids) which affect device quality. This problem is exacerbated with decreased lateral device dimensions. Recently, the practice of placing a semiconductor device within a high temperature/high pressure chamber (known as isostatic pressing) has been employed to collapse such voids, causing them to fill with hot deposited material. Isostatic pressing thus creates consistently higher quality devices through void elimination. High temperatures allow the deposited material to collapse and to flow more easily into voids and may also be employed to control crystal orientation.
Attempts to develop a commercially viable isostatic pressing chamber have failed because ceramic heaters (pervasively used in semiconductor processing because of their efficient heat transfer and electrically insulating properties) cannot survive even one isostatic pressing cycle. Specifically, in an isostatic pressing chamber having an upper heater and a lower heater, and having a wafer mounted proximate to the upper heater, the lower heater may fail by fracture during even the first high temperature/high pressure isostatic pressing cycle. Heater cracking requires heater replacement after each cycle, intolerably increases processing cost per semiconductor device and, moreover, generates particles which may destroy any devices being processed. Accordingly, a processing chamber must be developed that is able to withstand the repeated high temperature/high pressure cycling necessary to make isostatic pressing and its benefits a commercial reality.